This proposal prepared by the Harvard University Chemistry Department is intended to secure funds to purchase a mass spectrometer with electrospray ionization (ESI) and liquid chromatography (LC) mass spectrometry (MS) capabilities. The new spectrometer will expand the services offered by the existing Mass Spectrometry Facility, which does not have any LCIMS capability at present. The new machine will be used primarily to examine samples not amenable to analysis with the existing instrumentation. These materials fall into two broad classes. First, many species of interest have molecular weights too large for mass spectrometry with conventional ionization techniques. These samples include polypeptides and proteins, polynucleotides and high-molecular-weight polymers. The second class are nonvolatile materials not amenable to FAB ionization, either because of their insolubility in FAB matrices or because of artifacts generated in the FAB ionization process. These latter materials are principally organometallic compounds, many of which are models for catalysis.